Environmental Hydrodynamics

The environmental monitoring and modeling research is based on the use of the latest information on physical oceanography, hydraulic engineering and computer science for predicting the movement and mixing of fresh and salt waters and the constituents they carry. The fate and transport of sediments are an integral component of this research area. The approach to the research is designed to take advantage of the rapidly evolving high performance computational and communications technologies.

A wide range of models and processing tools, including visualization and animation routines, are constantly being developed and applied to problems associated with port security (environment sensing), beach erosion, marine construction and operations (ferry route optimization, desalination facilities, power plants, dredging), oil and gas exploration (spill response, design conditions), water quality (fresh water withdrawals), sediment and contaminate transport, municipal and industrial intakes/outfalls, off-shore dumping and storm surges. Modeling and observing systems for estuarine and coastal ocean nowcasts and forecasts are being constantly refined to provide the most accurate realizations possible of the marine environment.

The basis of the modeling systems is the Princeton Ocean Model (POM). POM is a sigma coordinate, free surface, primitive equation ocean model which includes a turbulence sub-model. It was initially developed in the late 1970's by Blumberg and Mellor with subsequent contributions from others. The model has been used for modeling of estuaries, coastal regions and open oceans.

ECOMSED, the Estuarine and Coastal Ocean Model, is a three-dimensional hydrodynamic and sediment transport computer code developed by HydroQual for application to marine and freshwater systems. The component models are designed to execute in conjunction with each other so that output from one model is directly linked to the other models. The models share the same numerical grid structure and underlying numerical solution techniques.

The development of ECOMSED has its origins in the mid-1980's with the creation of the Princeton Ocean Model followed by an upgraded version called ECOM for shallow water environments such as rivers, lakes, estuaries and coastal oceans. In the mid-1990s, concepts for sediment resuspension and settling developed by W. Lick at the University of California, Santa Barbara were incorporated within the ECOM modeling framework.

We are working on developing new, very flexible versions of ECOMSED/POM that can be reconfigured without recompilation. In addition, the new versions of the code will be significantly faster, more easily run, with new, easily learned graphical tools to visualize the data. Parallel performance will be much higher than on current versions.

Introduction to ECOMSED - Development History

The development of ECOMSED has its origins in the mid 1980s with the creation of the Princeton Ocean Model (Blumberg and Mellor, 1987) at Princeton University and its version for shallow water environments - rivers, bays, estuaries and the coastal ocean and reservoirs and lakes - named ECOM (Blumberg, 1996) at HydroQual, Inc.

In the mid 1990s, concepts for cohesive sediment resuspension, settling and consolidation (Lick, et al., 1984) were incorporated within the ECOM modeling framework by Stevens Professor Alan Blumberg and colleagues from HydroQual. During the last several years, ECOMSED was enhanced to include generalized open boundary conditions, tracers, better bottom shear stresses through a submodel for bottom boundary layer physics, surface wave models, noncohesive sediment transport, and dissolved and sediment-bound tracer capabilities. The code has been reconfigured to be easily ported to almost any computer system, from PCs to workstations to super mainframes. Model performance has been evaluated by appealing to a large series of simple test cases designed to isolate specific processes and by application of the model to many real-world situations. There have been over 350 journal articles written that are based on the use of the various POM and ECOMSED submodels. At present, Professor Blumberg works with students and staff at Davidson Laboratory to apply ECOMSED in very high resolution, and on new algorithms and optimizations, keeping ECOMSED and POM in the forefront of world-class hydrodynamic models. He also continues his collaboration with HydroQual where model enhancements to address practical environmental problems are developed.

Examples

To see some examples of ECOMSED in use, view the page on sample homework problems from a recent graduate class

The ECOMSED model is capable of simulating the transport and fate of suspended sediments, dissolved tracers and neutrally-buoyant particles in estuarine and coastal ocean systems. A wide variety of problems concerning water optics and spill tracking can be studied using the model due to the various options built into ECOMSED. Capabilities of the model include:

  1. runtime computed (internal) or pre-computed (external) hydrodynamics
  2. cohesive and non-cohesive sediment transport
  3. sediment-bound tracer transport (conservative or first-order decay)
  4. dissolved tracer transport (conservative or first-order decay)
  5. neutrally-buoyant particle tracking
  6. inclusion of wind wave effects on hydrodynamics and sediment transport.

Dr. Alan Blumberg, the coauthor of POM and the driving force behind ECOMSED is on faculty at Davidson Laboratory. We are doing exciting work in improving the hydrodynamics model in a number of ways.

Estuaries

When low tides drain the estuary goldSmall intersecting ripples far awayRipple about a bar of shifting sandsNorth Coast Recollections,John Betjeman

What is an estuary?

An estuary is a semi-enclosed coastal body of water which has a free connection to the open sea and within which sea water is measurably diluted with fresh water derived from land drainage. Pritchard(1963)

The seaward portion of a drowned valley system which recieves sediment from both fluvial and marine soures and which contains facies influenced by tide, wave and fluvial processes. The estuary is considered to extend from the landward limit of tidal facies at its head to the seaward limit of coastal facies at its mouth. Dalrymple et al(1992)

An estuary is a semi-enclosed body of water that extends ot the effective limit of tidal influence, within which sea water entering from one or more free connections iwith the open sea, or any other saline coastal body of water is siginificantly diluted with fresh water derived from land drainage, and can sustain euryhaline biological species for either part or the whole of their life cycle. Perillo(1995)

Types of Estuaries

  • Coastal Plain Estuaries - Most commonly occurring, these estuaries form in river valleys when the water level rises. Also known as Drowned River Valleys. Characteristically, these estuaries are relatively narrow and shallow. Examples include Chesapeake Bay in Maryland.
  • Tectonic Estuaries - Formed by the folding or faulting of land, these types of estuaries are found along fault lines. The San Francisco Bay area is one example of this type.
  • Bar-built Estuaries - Formed either by a shallow bay or laggoon which is protected from the open sea by a bar or barrier island, or by the connection of an inland body of water to the sea from land subsidence. Expamples of this type can by found along the North Carolina shoreline Coast
  • Fjords - These estuaries are formed from the cessation of glacial movements. As the glacier stops and melts it leaves a long deep channel protected from the open sea by a sill of deposited sediment that had been pushed by the glacier. Examples can be found in Northern Europe, Canada, Alaska and Greenland.

Some facts about estuaries

  • 1 in 6 jobs in United States Linked to coastal ocean and estuaries
  • Estuaries provide habitat for 75% of commercial fish catch and 80-90% of recreational fish catch
  • 60% of the worlds population lives near an estuary
  • 66% of the largest cities in the world are located on estuaries

Threats to our estuaries

  1. Pollution - As the estuary is generally represented by a increase in width at the end of a river, there is an accompanying decrease in water velocity. This allows for sediments within the water to settle and accumulate in the estuary. In this manner, the estuary acts as a filter for the water entering the ocean. This accumulation of sediments and pollutions is often harmful to the organisms in the estuary, as well as necessitating the closing of fishing beds and shellfish harvesting.
  2. Overuse - Due to the increase in land requiremnts, wetlands are continuously destroyed in order to meet increased demands for residential and industrial spaces.

Physics of Estuaries

The physics of estuaries are described by an amalgomation of various equations, including but not limited to the Navier-Stokes equations, continuity equations, vertically integrated equations, and Salt Flux equations. Click on the Links to see each equation

Computational Models of Estuaries

Estuaries are very complex entities. There are many forces, and depending on the balance between them, the estuary may totally change its profile. Salinity intrudes from the ocean, but is driven back by fresh water running out through rivers. Tides push water from the ocean inland, and then pull it back again, exchanging water somewhat as they do. Irregularly contoured land, and/or rough bottom surface may keep water from moving as freely back and forth. Wind can cause surface currents, and indirectly induce other counter-currents. Changing depth contours can slow water flow in some areas, speeding it up in others. Sediment from upstream can fill in and change the depth over time, and a big storm can redistribute that sediment. Last, the Coriolis force can curve currents if the estuary is wide enough.

All these forces make studying estuaries interesting, and make exact analytical solutions impossible -- everything affects everything else. These problems are highly nonlinear, and it is difficult to predict when a little more of one force will tip the solution in a totally different direction.

The following link contains homework problems given in a recent graduate class, with beautiful graphics showing the behavior of water in four classic problems. There are also movies of these problems

Since Davidson Laboratory is on the Hudson River, our focus is often on the New York/New Jersey Estuary system. The following are Links to various images from our fieldwork and simulations.

At Davidson Laboratory, we have ongoing projects studying how to make faster, better computational models of the ocean. The underlying algorithms have been changed very little since Prof. Alan Blumberg first wrote them as a postdoc, despite numerous people trying to run them in parallel for faster computation. We are now investigating ways of streamlining these algorithms, making them run faster both on single processors and in parallel.

As a side-effect of our research into improving the algorithms of ECOMSED and POM, we have discovered some interesting facts about the density of water.

Current research thrusts are in the following areas:

  • Environmental Circulation and Sediment Transport Modeling
  • Wave dynamics and Modeling
  • Cohesive and Non-cohesive Sediment Physics and Transport Modeling
  • Contaminated Sediments-Fate and Transport Modeling
  • Range of Predictability and Uncertainty Quantification
  • Beach Erosion Processes and Modeling
  • Solute and Suspended Solute Transport Modeling
  • Ocean Outfall/Intake Design Monitoring and Modeling
  • Mixing Zone Delineation